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CIT 470: Advanced Network and System Administration

CIT 470: Advanced Network and System Administration. Distributing Files. Topics. Sharing Files Copying Files: push vs pull rsync Network Filesystems Administering NFS. Sharing Files. System files Centralize administration: shared logins, naming. Solution: copy files between machines.

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CIT 470: Advanced Network and System Administration

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  1. CIT 470: Advanced Network and System Administration Distributing Files CIT 470: Advanced Network and System Administration

  2. Topics • Sharing Files • Copying Files: push vs pull • rsync • Network Filesystems • Administering NFS CIT 470: Advanced Network and System Administration

  3. Sharing Files System files • Centralize administration: shared logins, naming. • Solution: copy files between machines. • Alt Solution: Directory services (LDAP.) User files • User wants access to files on every machine. • Solution: copy files between machines. • Alt Solution: Network filesystems. CIT 470: Advanced Network and System Administration

  4. Copying Files Advantages • No network services to set up. • Works everywhere. Decisions • Push vs Pull Solutions • ftp • wget • ssh • rsync CIT 470: Advanced Network and System Administration

  5. Automating ftp #!/usr/bin/expect spawn ftp mysvr.nku.edu expect “username:” send “ftp\r” expect “password:” send “expect@client.nku.edu\r” expect “ftp>” send “bin\r” expect “ftp>” send “prompt\r” expect “ftp>” send “mget *\r” expect “ftp>” send “bye\r” expect eof CIT 470: Advanced Network and System Administration

  6. wget Non-interactive file retrieval • Protocols: ftp, http, https. • Useful for automating file xfer in scripts. • Ex: wget http://svr.nku.edu/files/etc/hosts Options • Authentication and proxying. • Quiet • Recursive: follows links in HTTP documents. • Resume • Retries CIT 470: Advanced Network and System Administration

  7. ssh-based copying • Securely copy files to/from another host. • Limitations • scp copies list of files on command line (-r for recursive) to single destination. • Copies all files, not just updated files. • Must share keys to authenticate securely. • sftp most suited for manual fs exploration. CIT 470: Advanced Network and System Administration

  8. rsync • Synchronizes file trees between machines. • Advantages • Makes remote tree identical to local one. • Only copies files that have been changed. • Only copies file parts that have been changed. • Useful for local mirroring, staging dirs, &c too. • Transport Mechanisms • rcp: insecure, avoid. • scp: secure, commonly used. • rsync: rsync protocol, best for anonymous use. CIT 470: Advanced Network and System Administration

  9. rsync over ssh Push rsync -av -e ssh local root@svr:test Pull rsync -av -e ssh root@svr:test local Test rsync -avn -e ssh root@svr:test local CIT 470: Advanced Network and System Administration

  10. Fine tuning rsync Deleting removed files (be careful) rsync -av -e ssh --delete local root@svr:test Excluding unwanted files. On the command line rsync -av -e ssh --exclude=“*.bak” --exclude=".?*.sw?” local root@svr:test Through a file rsync -av -e ssh --exclude-from=~/exclude-list local root@svr:test CIT 470: Advanced Network and System Administration

  11. rsync server Setting up an rsync server • Create an rsyncd.conf file. • Server: rsync --daemon • Client: rsync svr::public/new.tgz . Simple, but be careful about security. • Often secure by DNS name or IP address. • Can secure by user with rsync secrets file. • No encryption (need to use ssh tunnel.) CIT 470: Advanced Network and System Administration

  12. rsyncd.conf # "global-only" options syslog facility = local5 # global options which may also be defined in modules use chroot = yes uid = nobody gid = nobody max connections = 20 timeout = 600 read only = yes # module: [public] path = /home/rsync comment = Tarball archive hosts allow = *.nku.edu, 10.18.3.0/24, 10.30.4.4 ignore nonreadable = yes refuse options = checksum dont compress = * CIT 470: Advanced Network and System Administration

  13. Other File Distribution Systems rdist • Older tool like rsync but slower, fewer features. unison • Unlike rsync, handles updates on both sides. • Conflict resolution like CVS to handle case when file is modified on both sides. cfengine • Maintains state of system according to policy. • Copies files as needed to meet policy. CIT 470: Advanced Network and System Administration

  14. Automating File Copying Write a cron job. • Script can verify data before/after copy too. How to deal with many machines? • Add a random delay using a simple script: #!/usr/bin/perl # sleep 0-15 minutes (0-900s) sleep rand() * 900; CIT 470: Advanced Network and System Administration

  15. Network Filesystems Idea: Use filesystem to transparently share files between computers. Solution: • Client mounts network fs as normal. • Client filesystem code sends packets to server(s). • Server responds with data stored on a regular on-disk filesystem. CIT 470: Advanced Network and System Administration

  16. NFS Network File System • Transparent, behaves like a regular UNIX filesystem. • Uses UNIX UIDs,GIDs,perms but can work on Win. • Since NFS is stateless, file locking and recovery are handled by rpc.lockd and rpc.statd daemons. Security • Server only lets certain IP addresses mount filesystems. • Client UIDs have same permissions on server as client. • Client root UID is mapped to nobody, but • Root can su to any client UID to access any file. CIT 470: Advanced Network and System Administration

  17. CIFS Microsoft Network Filesystem • Derived from 1980s IBM SMB net filesystem. • Originally ran over NetBIOS, not TCP/IP. • \\svr\share\path Universal Naming Convention • Auth: NTLM (insecure), NTLMv2, Kerberos Implementation • MS Windows-centric (filenames, ACLs, EOLs) • Samba: UNIX client and server software. CIT 470: Advanced Network and System Administration

  18. AFS Distributed filesystem • Global namespace: /afs/abc.com/vol_home1 • Servers provide one or more volumes. • Volume replication with RO copies on other svrs. Cells are administrative domains within AFS. • Cells contain multiple servers. • Each server provides multiple volumes. Security • Kerberos authentication • ACLs with user-administered groups CIT 470: Advanced Network and System Administration

  19. NFSv4 New model of NFS • Only one protocol (no separate mount,lock,etc.) • Global namespace. • Security (ACLs, Kerberos, encryption) • Cross platform + internationalized. • Better caching via delegation of files to clients. CIT 470: Advanced Network and System Administration

  20. Adminstering NFS • NFS Versions • Using NFS • NFS Services • Server and Client Configuration • Automounter • Security • Performance CIT 470: Advanced Network and System Administration

  21. NFS Verions v2 (1984) UDP 32-bit v3 (1992) TCP 64-bit. v4 (2000) Distributed, x-platform, security. CIT 470: Advanced Network and System Administration

  22. Client Start portmap … … … Mount filesystems. Server Start portmap Start NFS services. Configure exports. Export filesystems. Using NFS CIT 470: Advanced Network and System Administration

  23. NFS Services portmap — RPC service for Linux portmap nfs — NFS file server processes. rpc.mountd rpc.rquotad nfsd nfslock — Optional file locking service. rpc.statd CIT 470: Advanced Network and System Administration

  24. NFSv2/3 Processes rpc.mountd — Handles client mount requests. rpc.nfsd — NFS server processes. rpc.lockd — Process for optional nfslock service. rpc.statd — Handles server crashes for nfslock. rpc.rquotad — Quotas for remote users. CIT 470: Advanced Network and System Administration

  25. rpcinfo > rpcinfo -p program vers proto port 100000 2 tcp 111 portmapper 100000 2 udp 111 portmapper 100021 1 udp 32774 nlockmgr 100021 1 tcp 34437 nlockmgr 100011 1 udp 819 rquotad 100011 2 udp 819 rquotad 100011 1 tcp 822 rquotad 100011 2 tcp 822 rquotad 100003 2 udp 2049 nfs 100003 3 udp 2049 nfs 100003 2 tcp 2049 nfs 100003 3 tcp 2049 nfs 100005 2 udp 836 mountd 100005 2 tcp 839 mountd 100005 3 udp 836 mountd 100005 3 tcp 839 mountd CIT 470: Advanced Network and System Administration

  26. NFSv4 Processes nfsd — NFSv4 server processes. Handles mounts. rpc.idmapd — Maps NFSv4 names (user@domain) and local UIDs and GIDs. Uses /etc/idmapd.conf. rpc.svcgssd — Server transport Kerberos auth. rpc.gssd — Client transport Kerberos auth. CIT 470: Advanced Network and System Administration

  27. Server Configuration • Configure /etc/exports List filesystems to be exported. Specify export options (ro, rw, etc.) Specify hosts/networks to export to. • Export filesystems. exportfs • Start NFS server (if not already started) service portmap start service nfs start CIT 470: Advanced Network and System Administration

  28. /etc/exports Format: directory hosts(options) Options ro, rw Read-only, read-write. async Server replies before write. sync Save before reply (default) all_squash Map all users to anon UID/GID. root_squash Map root to anon UID (default) no_root_squash Don’t map root (insecure.) anon{uid,gid} Set anonymous UID, GID. Examples: /home *.example.com(rw,sync) /backups 192.168.1.0/24(ro,all_squash) /ex/limited foo.example.com CIT 470: Advanced Network and System Administration

  29. Client Configuration Manual mounting mount -t <nfs-type> -o <options>server:/remote/export/local/directory Mounting via /etc/fstab server:/remote/export/local/directory<nfs-type><options> 0 0 NFS Type is either nfs or nfs4. CIT 470: Advanced Network and System Administration

  30. Mount Options hard or soft — Error handling hard: NFS requests will uninterruptible wait until server back. soft: NFS requests will timeout and report failure. intr — NFS requests can be interrupted if server unreachable. nfsvers=2,3— NFS protocol version (not 4) noexec — Prevents execution of binaries. nosuid — Disables setuid for security. rsize,wsize=# — NFS data block size (default 8192) sec=mode — NFS security type. sys uses local UIDs and GIDs. krb5 uses Kerberos5 authentication. krb5i uses Kerberos5 authentication + integrity checking krb5p uses Kerberos5 auth + integrity checking + encryption. tcp, udp — Specifies protocol to use for mount. CIT 470: Advanced Network and System Administration

  31. Automounter Manages NFS mounts Automounter maps vs /etc/fstab. Mounts filesystems only when needed: Makes administering many filesystems easier. Improves startup speed. Provides uniform namespaces. Ex: mounts /home/home7 as /home on login. /etc/auto.master points to maps /home /etc/auto.home Maps describe mounts * -fstype=nfs4,soft,intr,nosuid server:/home CIT 470: Advanced Network and System Administration

  32. Security Limit which hosts have access to filesystems. • Specify hosts in /etc/exports. • Use iptables to limit which hosts can use NFS. Limit mount options • Default to ro unless writes are necessary. • Disable suid and execution unless needed. • Map root to nobody. Block NFS at network firewalls. • Block all protocols, not just port 2049. Use NFSv4 with Kerberos auth + encryption. CIT 470: Advanced Network and System Administration

  33. Performance Measuring performance nfsstat /proc/net/rpc/nfsd Optimizations • Increase the block size. Problem: fragments? • Set the async option on mounts. • Faster network card. • Faster disk array. • NVRAM cache on array to save NFS writes. CIT 470: Advanced Network and System Administration

  34. References • Michael D. Bauer, Linux Server Security, 2nd edition, O’Reilly, 2005. • cfengine, http://www.cfengine.org/ • Mike Eisler, Ricardo Labiaga, Hal Stern, Managing NFS and NIS, 2nd edition, O’Reilly, 2001. • expect, http://expect.nist.gov/ • Aeleen Frisch, Essential System Administration, 3rd edition, O’Reilly, 2002. • Evi Nemeth et al, UNIX System Administration Handbook, 3rd edition, Prentice Hall, 2001. • NFS HOWTO, http://nfs.sourceforge.net/nfs-howto • RedHat, Red Hat Enterprise Linux 4 System Administration Guide, http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guide/, 2005. • RedHat, Red Hat Enterprise Linux 4 Reference Guide, http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref-guide/ch-nfs.html, 2005. • rsync, http://www.samba.org/rsync/ • Unison, http://www.cis.upenn.edu/~bcpierce/unison/ CIT 470: Advanced Network and System Administration

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